hi, I think there is a bug in ISPC regarding changing between fpm versions. tested on ubuntu 16.04 - nginx - ISPC3.11 and 3.12 (found an old post on stackoverflow that seemed to have the same issue but was not well detailed - so it could be that this is an issue for a long time. It is not the most common situation tbh...) effect: fpm unit will not start with error: systemd: Starting The PHP 7.1 FastCGI Process Manager... php-fpm7.1: [23-Jul-2018 08:05:04] ERROR: An another FPM instance seems to already listen on /var/lib/php7.0-fpm/web140.sock php-fpm7.1: [23-Jul-2018 08:05:04] ERROR: FPM initialization failed systemd: php7.1-fpm.service: Main process exited, code=exited, status=78/n/a systemd: Failed to start The PHP 7.1 FastCGI Process Manager. steps to reproduce: have a mirror setup of ispc running multiple php versions create a webhost and set a php version (tested only with php-fpm) change php version to a different value than before the problem will only occur on the mirror server not on the master (which can have a devious effect in a hot spare situation if you dont notice..) the change of php version causes a new pool file to be created in /etc/php/v.m/fpm/pool.d/webx.conf there we define which socket file should be used the bug seems to be that after php version is changed to a new value the old pool file is only removed on the master but not on the mirror, so the new file which is created with the same socket file will cause the problem. the first fpm process wins the socket file the other one can not have it.